Internal combustion engine manufactures strive to produce engines which produce low levels of harmful exhaust emissions and high levels of fuel economy. In doing so, it may be beneficial to run the engine on a mixture which includes a very lean air/fuel ratio as well high levels of exhaust gas recirculation (EGR) that are to be ignited in the combustion chamber. Strategies are being investigated by engine manufactures to increase the capability of the ignition systems of the engines to reliably ignite the mixture in each combustion chamber. One strategy is to increase the number of ignition sites within each combustion chamber. Historically, only one spark plug has been provided for igniting the mixture in each combustion chamber. More recently, two spark plugs have been provided in some engines for igniting the mixture in each combustion chamber. In order to provide a spark-generating current to each of the two spark plugs in a single combustion chamber, each spark plug may be provided with its own distinct ignition coil. Alternatively, a single ignition coil as shown in U.S. Pat. No. 7,148,780 which is commonly assigned and incorporated herein by reference in its entirety may be used to provide a spark-generating current to both spark plugs. While two spark plugs per combustion chamber may be sufficient for some applications, current developments have led to configurations that require three spark plugs per combustion chamber. The conventional approach to providing a spark-generating current to each of the three spark plugs is to provide each of the three spark plugs with its own distinct ignition coil. However, due to packaging size, controller requirements, and costs associated with three distinct ignition coils, it may be desirable to provide a single ignition coil that provides a spark-generating current to each of the three spark plugs.
What is needed is an ignition coil which provides a spark-generating current to three spark plugs of a single combustion chamber of an internal combustion engine.